The Stovebolt Site Forums The Parking Lot Big Bolts Help, is my rear differential ok?

I was looking at my 1970 c50 dump today, I went to move the drive shaft by hand ( truck in neutral ) and I noticed that the rear differential has a TON! of backlash. I know that this is a old truck with a ton of miles, but if this was in a car it would be junk. The pinion turns about 3/4 to a inch before it hits the ring gear. That's what it feels like. How much is normal? I don't have much experiance with the big stuff, this is my first. I am only planning to use this truck for local runs 15 to 20 mile radious, but if this thing needs a rear end I cannot afford it. and I don't want to keep spending money on it. I have not driven it on the road yet, ( not registered ) seems ok on my short back road. This is a single speed rear, NOT a 2 speed. hoping you guys will say it is just old and should be ok for the limited use I 'll give it.

Give it a try, if it is quiet and performs OK, then use it, you won't be far from home if it fails.

I have noticed what seems like lots of backlash on a number of differentials when just turning the driveshaft, and they have worked fine, so perhaps this is not an accurate way of diagnosing excessive backlash?

By just grabbing the driveshaft you would also be taking up the slack in the spider gears, axle shafts in the side gears, and the axle shafts in the hubs, this may all add up to feel like a lot, and the pinion portion of it may be small and OK?

Grigg

the only way to correctly measure backlash is by taking the diff cover off or third member out and setting up a dial indicator and measureing it cause like grigg said when you turn the driveshaft your are also talking up the play in the pinion/side gears, which can make backlash seem excessive
Nate

Yes, I know that this is correct way to check, but I am not looking to take this apart, I am hoping it's like Grigg said. I am going to take out the fill plug in the rear and with a small light try to see if that is what is happening, and it's not ALL play between the ring and pinion.

While you have that fill plug out you might stick a large screwdriver in there and lever it against the ring with one hand and reach under and try turning the yoke then.
Like these other folks have stated, there's a lot of other places for play to add up ut still be fine. My old beast has a load of play in it, yet wear on the mating surfaces on the ring & pinion are within limits.

not much happens to a single speed rear except making noise. If it isn't making any grinding noises, drive it. If it sings a little, so what. 50 years ago when lube wasn't very good, just about all truck rears whined.

They don't have to be a big bolt to have lots of back lash and that doesn't mean that it is bad. I wouldn't worry about it at all.